Distributed power train operation supplies motive power from a lead locomotive and one or more remote locomotives spaced apart from the lead locomotive in a train consist. Each lead and remote locomotive includes an air brake control system for controlling braking operations and a communication system for exchanging information between lead and remote locomotives over a communication link. A brake pipe fluidically interconnects each of the locomotives and rail cars of the train wherein modulation of a fluid flow, such as a fluid pressure in the brake pipe, is conventionally used to indicate desired braking operations. Remote locomotive braking operations may be controlled responsive to sensed brake pipe flow conditions at the respective remote locomotives.
Brake application is typically accomplished by venting, or reducing a pressure in the brake pipe. However, brake pipe venting at only the lead locomotive of a train requires propagation of the corresponding brake pipe pressure reduction along the length of the train, thus slowing brake application at rail cars and remote locomotives near the end of the train. In distributed power trains, braking is more effectively accomplished by venting a brake pipe at both the lead and remote locomotives of the train, thus accelerating the brake pipe venting and the application of brakes, throughout the train. Accordingly, the lead locomotive may separately command braking operations of the remote locomotives over the communication link to achieve more effective braking of the train.
In addition to controlling braking according to brake pipe flow conditions, each remote locomotive may be capable of independently controlling a fluid flow in the brake pipe responsive to a sensed brake pipe flow condition. For example, each remote locomotive may be capable of charging the brake pipe responsive to a sensed brake pipe fluid leak. During certain disturbed power train operations, it is desired to limit a remote locomotive's ability to control brake pipe fluid flow. For example, during brake pipe charging after a train brake application and corresponding brake release, a brake pipe flow indication at the remote locomotive may be ignored, or masked, to prevent the remote locomotive from interfering with brake pipe charging.